Neurons contact each other mostly by synaptic transmission at synapses. Synaptic transmission relies on vesicle exocytosis, i.e., fusion of vesicles with the plasma membrane and release of transmission. To maintain vesicle exocytosis, fused vesicles must be retrieved, or endocytosed, to form new vesicles for the second round of exocytosis. My goal is to improve our understanding on the cellular and molecular mechanisms underlying synaptic vesicle exocytosis and endocytosis, which are the building block for synaptic transmission and thus the signaling process in the neuronal network. [unreadable] [unreadable] My progress in the last year is listed in the following. First, we found two modes of fusion, full collapse and kiss and run mode (Nature, 2006). The kiss-and-run mode may release transmitter slowly depending on its fusion pore size, and thus provide a method to control synatic strength. Second, we found that quantal size, the most fundamental parameter that determines synaptic strength, is regulated by the glutamate concentration inside the vesicle (J Neurosci, 2007). Third, we resolved the final step of the bulk endocytosis, the fission process, and provided the first measurement of the fission rate at synapses (PNAS, 2007).